1. Field of the Invention
The present invention relates to contactless radio data communications that use contactless identification tags and a reader/writer device, and more particularly, to contactless identification tags, data communication systems and contactless identification tag control programs, which are suitable for setting the sequence of communications when a plurality of contactless identification tags are present in the range of communication of a reader/writer device.
2. Description of Related Art
Japanese Patent Document 2814974 describes contactless IC cards and a data communication device, as a data communication technology which sets an appropriate sequence of communications for a reader/writer device and a plurality of RF-ID tags. When the reader/writer device disclosed in Japanese Patent Document 2814974 communicates with a contactless IC card via radio communications, and confirms an interference at an initial communication with the contactless IC card, the reader/writer device sends a notification of the event to multiple contactless IC cards that are present in its range of communication. In the meantime, the contactless IC card generates a random number according to a random number generation algorithm stored in a memory, as a processing preparation at the time of interference, and decides in advance a number (one of 0-9) for a transmission slot (which is a slot divided by time).
After receiving the notification of interference from the reader/writer device, the contactless IC card returns a response to the reader/writer device according to the number of the transmission slot. Further, the contactless IC card sets a number for a transmission slot according to a procedure similar to the above for preparation of the next interference. In the meantime, if the reader/writer device confirms an interference again based on responses from contactless IC cards, the reader/writer device sends a notification of the interference to the contactless IC cards. The processes described above are repeated until there is no interference.
However, according to this conventional technology, random numbers generated by the random number generation algorithm are used as they are (for example, the last digit of each random number is used) for setting numbers for transmission slots, such that the event probability of each of the numbers set to each of the contactless IC cards depends on the event probability of each number generated according to the random number generation algorithm. Therefore, the same number may be set many times to multiple contactless IC cards depending on the performance of the random number generation algorithm. As a result, there are possibilities that interferences may be caused many times, and it may take a long time to cancel the interferences.
The present invention overcomes these unsolved problems of the conventional technology, and provides contactless identification tags, data communication systems and contactless identification tag control programs, which are suitable for setting a sequence of communications where a plurality of contactless identification tags are present in the range of communication of a reader/writer device.